The invention relates to disc drive storage systems using accelerometers. In particular, the invention relates to correction for rotational acceleration in a disc drive storage system.
Disc drives have problems when rotational shock or vibration forces are applied. The rotational shock can move a read/write head away from the center of the desired track on a disc. This can cause either an error or a delay in transferring data. The use of an accelerometer for correction, however, reduces problems encountered with rotational vibration.
The use of accelerometers in disc drives is known. In U.S. Pat. Nos. 6,018,431 and 5,923,487 Carlson et al., for example, a disc drive includes a shock evaluator or sensing circuit with resettable threshold shock values to account for changes in operating conditions. In U.S. Pat. No. 5,663,847 Abramovitch, a disc drive includes an acceleration responsive sensor that is sampled at a different sampling rate than the position error signal.
It is difficult, however, for the head-positioning servo controller to complete computations associated with using an accelerometer without excessively delaying computations associated with responding to servo positioning command inputs from an associated computer system. Further, when the disc drive experiences rather large transient rotational shocks, the vibration correction calculations can tend to overcorrect and cause significant errors in the performance of the servo controller functions.
Disc drives, particularly those used in battery-powered portable computers, have significant electrical power constraints that preclude solving these problems using larger or faster controllers that draw excessive amounts of power.
A method and an apparatus are needed, within the power constraints of a disc drive, to correct for rotational vibration while avoiding unduly delaying performance of servo control calculations. A method and apparatus are also needed that avoid overcorrecting for transient rotational events.
Disclosed is a method and circuit that correct for rotational vibration disturbances of a head position in a disc drive. The circuit includes a servo controller that controls a positioning motor for the head as a function of servo data from the head. The circuit also includes a rotational vibration (RV) controller that also controls the positioning motor for the head as a function of an output of an accelerometer and multiple sets of adjustable gains xe2x80x9cgixe2x80x9d in the rotational vibration controller.
The accelerometer output indicates vibration and is coupled to the RV controller. The accelerometer output is compared to an acceleration threshold stored in the controller. If the acceleration is greater than the threshold, then a conditional branch is made to provide rotational vibrational correction to the positioning motor.
The controller updates one set of the adjustable controller gains xe2x80x9cgixe2x80x9d within a computational time limit after a first execution of servo controller code. The controller preferably updates a second set of the adjustable controller gains xe2x80x9cgixe2x80x9d within the computational time limit after a second execution of servo controller code.
Additional features and benefits will become apparent with a careful review of the following drawings and the corresponding detailed description.